Enhanced Upper Ocean Warming Projected by the Eddy‐Resolving Community Earth System Model

Abstract Ocean warming is a key factor impacting future changes in climate. Here we investigate vertical structure changes in globally averaged ocean heat content (OHC) in high‐ (HR) and low‐resolution (LR) future climate simulations with the Community Earth System Model (CESM). Compared with observation‐based estimates, the simulated OHC anomalies in the upper 700 and 2,000 m during 1960–2020 are more realistic in CESM‐HR than ‐LR. Under RCP8.5 scenario, the net surface heat into the ocean is very similar in CESM‐HR and ‐LR. However, CESM‐HR has a larger increase in OHC in the upper 250 m compared to CESM‐LR, but a smaller increase below 250 m. This difference can be traced to differences in eddy‐induced vertical heat transport between CESM‐HR and ‐LR in the historical period. Moreover, our results suggest that with the same heat input, upper‐ocean warming is likely to be underestimated by most non‐eddy‐resolving climate models.